A variety of pump systems are employed for delivering therapeutic fluid to a patient. Such systems typically employ reservoirs having rigid surfaces, such as a metal bellows or a glass vial with a moving plunger or syringe. Such reservoirs or associated accessory components, such as an actuator, can be expensive to manufacture, and thus are not ideal for a low cost or disposable pump. For example, systems with rigid vials employing a piston to pump fluid from the vial must have sufficiently powerful motors or actuation mechanisms to overcome stiction and negative pressures associated with dispense in such systems, but should also be finely tailored to deliver precise amounts of therapeutic fluid. Systems with such powerful and precise electrical and mechanical components can be expensive to manufacture.
Some pump systems employ conformable reservoirs or flexible bags, e.g. bladders, which may be amenable to lower manufacturing costs. Unlike rigid vials, flexible bags allow for neutral pressure dispense or positive pressure dispense, if the bag is elastomeric. Accordingly, more energy efficient and lower cost pumping mechanisms or flow control mechanisms may be employed with conformable reservoir systems relative to rigid vial pump systems. However, such conformable reservoirs lack the mechanical protection afforded by rigid reservoirs. In addition, the costs associated with handling and filing conformable reservoirs tend to be higher than their rigid counterparts or require difficult filling procedures to be carried out by the end user. Further, conformable reservoirs tend to suffer from drawbacks associated with the ability of molecules to cross the material of the reservoir. Such drawbacks include permeation loss of one or more component of the therapeutic fluid or ingress of unwanted molecules into the therapeutic fluid. Permeation can significantly reduce shelf life of therapeutic fluids stored in conformable bladders relative to rigid counterparts.
Some therapeutic fluids, such as those containing insulin are often stored for years prior to being administered to a patient. Accordingly, permeation issues can present significant challenges for storage and subsequent delivery of such therapeutic fluids via pump systems in a cost effective manner.